1. Field of the Invention
The present invention relates to a method of positioning an image frame for detecting an image frame edge on a photographic film based on a quantity of transmitted light passing through the photographic film which is carried on a guide path, and positioning the detected image frame edge at a predetermined position.
2. Description of the Related Art
A photoprinter is provided with a negative carrier at a printing position for, in order positioning image frames of a negative film in order at the printing position after development of the film. The negative carrier comprises a base and a cover body which can open and close with respect to the base. The base has a negative film guide path provided with a printing opening corresponding to an image frame. The guide path has driving rollers at positions corresponding to the vicinities of both the transverse edges of the negative film. The driving rollers are rotated by a driving force of a pulse motor. The cover body is provided with idle rollers paired with the driving rollers to hold the negative film between the driving rollers and idle rollers. Thus, these paired rollers are allowed to hold and carry the negative film along the guide path when the cover body is closed and the negative film is inserted into the negative carrier from one side thereof.
A detecting apparatus for detecting an image frame edge is mounted upstream the printing opening of the guide path. The detecting apparatus, as disclosed in Japanese Patent Application Laid-Open No. 3-11329, is provided with a cold-cathode tube or a halogen lamp at the rear side of the guide path, and a slit hole formed in the guide path. In the detecting apparatus, each image frame of the negative film on the guide path is irradiated with a light emitted from the cold-cathode tube or halogen lamp.
The cover body is provided with a light receiving sensor corresponding to the slit hole so that light transmitted through the negative film can be received by the sensor. Transmission density of the negative film can be calculated based on quantity of received light detected by the light receiving sensor. Generally, a base portion of the negative film has a low transmission density while the negative film has a high transmission density within the range of the image frame. It is possible to compare a difference between the transmission density of the base portion and that of the image frame with the predetermined transmission density to detect a boundary between the image frame and the base portion, i.e., the image frame edge. The image frame edge allows the respective image frames of the negative film to be positioned at the printing position.
Therefore, it is possible to position each image frame of the negative film at the printing position automatically and accurately even if the pitches of the respective image frames recorded on the negative film are fluctuated depending on feeding errors in photographing by a camera. Thus, the feeding error due to a quantitative feeding can be eliminated. In addition, the negative carrier itself can be simply constructed because it is not necessary to detect a notch provided for each image frame.
In such a control for positioning, a front edge of each image frame generally serves as a reference edge when it is normally spaced from the preceding image frame. If abnormally spaced, it is detected whether or not the back edge of the image frame is normally spaced from the preceding image frame. If normally spaced, the back edge can be used as the reference edge. If neither front nor back edges are normally spaced, the negative film is quantitatively fed on the basis of a state where the preceding image frame is positioned.
However, when the quantitative feeding is carried out, it is not always ensured that an appropriate relation is provided between a position of the image frame to be positioned and that of the preceding image frame. Therefore, the positioning may not be accurately performed. Also, repetition of the quantitative feeding causes an accumulated error so that the positioning point may be further deviated.
In recent years, it has been desired to provide a camera for photographing on a so-called panoramic size image frame as well as so-called standard size image frames such as a full-size image frame and a half-size image frame. A printed photographic paper on which the panoramic size image frame has been printed is longer in the side corresponding to the longitudinal direction at the negative film than a photographic paper on which the full-size image frame has been printed. The panoramic size image frame has a shorter transverse length of the negative film than that of the standard size image frame, and is defined in a narrower form than the full-size image frame. Accordingly, a negative film may include both the standard size image frame and the panoramic size image frame.
However, the size of the image frames can not be selected by the conventional negative carrier. Thus, the size should be selected depending on an operator's visual check.
In the conventional negative carrier, a negative mask suitable for each size of the image frame is employed, and mounted on the printing opening. In order to process the negative film including image frames in both sizes, the negative mask is switched according to the size of each image frame to be detected and positioned so that image frames can be printed in the order of the image frames recorded on the negative film.
However, in the conventional printing method, the negative mask should be frequently switched depending on a condition including each size image frame to reduce the process efficiency. Further, an operation to sort the printed photographic papers according to their sizes requires more time period and results in a poor efficiency.